The princess who's been held captive by the Demon Lord's army is scheduled to be executed by the Demon Lord's relentless torture!

After the decline of the once robust fields of science and technology, a new energy source known as magic fuels the modern era. Humanity creates forbidden biological weapons: Gears. Those Gears eventually stand against humanity in a rebellion. Although they manage to overcome in the struggle for survival known as the Crusades, humanity's losses are so great that even after several decades pass, their emotional wounds remain unable to fully heal. Sin Kiske, the child of a human and a Gear, heads to his father Ky and mother Dizzy's wedding ceremony. Their wedding breaks the ultimate taboo: a union between a human and a Gear. Even with the world at peace, it took many years for such a ceremony to come to fruition. Despite the complex array of emotions surrounding it, the wedding ceremony is met with blessings. When suddenly, a mysterious girl appears... The fated child inheriting Gear blood–and the mysterious girl who despises Gears. Their meeting would shake the world.

In the small village of Hinamizawa, Rika Furude and her friends live together in relative harmony. Beneath this mask of peace, however, lies a hidden darkness, one that Rika understands all too well. In this eternal summer, she has been witness to unspeakable horrors. Every time the clock resets, Rika must try to find the villain behind these senseless deaths before tragedy strikes again. However, trying to decipher a mystery when only half the clues are present proves time and again to be disastrous, and each time she believes that things will change, she inevitably fails. As the annual festival approaches, Rika begins her descent from hope to despair in her struggle to break the chains of fate entangling them all. [Written by MAL Rewrite]

The visual features the tagline, "I met you in my 17th summer ..." The "boy-meets-girl" story depicts how words and music bridge the gap between Cherry, a boy who is terrible at communicating with other people, and Smile, a girl who hides behind a mask. They meet in a mundane suburban shopping mall in a provincial city. Cherry always wears headphones and puts the feelings he cannot utter into his hobby, Japanese haiku poems. Smile always wears a mask to conceal her large front teeth, for which she has dental braces. As a popular video star, she streams a video about seeking "cuteness." (Source: ANN)